1. Field of the Invention
The present invention relates to a substrate inspection method that takes an image of a substrate, such as a semiconductor wafer, a substrate for a LCD, namely, a glass substrate for a liquid crystal display, for inspection, a substrate inspection system and a storage medium.
2. Description of the Related Art
A photolithographic process for fabricating a semiconductor device includes a coating process of coating a semiconductor wafer W (hereinafter, referred to simply as “wafer W), with a resist film, an exposure process of forming a predetermined pattern with optical radiation in the resist film, and a developing process of processing the exposed resist film to form a predetermined resist pattern. Those processes are carried out sequentially to form the predetermined resist pattern on the wafer W.
The wafer W processed by the series of photographic processes is carried into an inspection module included in a coating and developing system that carries out the coating and the developing process. A camera disposed in the inspection module forms an image of the surface of the wafer W. The image is displayed on an output screen. The picture displayed on the output screen is inspected for a macro defect inspection to see if the resist film is formed in a desired shape on the wafer W, to see if any defects are formed in the surface of the resist film and to see if any dust particles are sticking to the surface of the resist film. The construction of such an inspection module is mentioned in JP-A 2007-240519 (FIG. 4).
FIG. 16 shows a camera 1, namely, a pinhole camera, and a wafer W to be inspected. The cameral 1 is provided with a lens 11, and an image forming device 12, such as a CCD, having an image forming surface 13. In FIG. 16, a chain line indicates the optical axis of the camera 1, A1 indicates a point where the optical axis intersects the surface of the wafer W, and a two-dot chain line connecting the lens 11 and a point A2 on the wafer W nearest to the lens 11.
Referring to FIG. 16, an image of a part around the point A2 formed by the lens 11 is larger than an image of a part around the point A1. Consequently, a distorted image is formed on the image forming surface 12. A picture corresponding to the image formed by the image forming device 12 and displayed on the output screen is a distorted picture of the wafer W@. Usually, the picture displayed in the output screen is distorted and the degree of distortion is dependent on the three-dimensional relation between the camera 1 and the wafer W. Practically, the distortion of the picture displayed on the output screen is dependent on parameters inherent to the camera as well as on positioning parameters representing the positional relation between the camera 1 and the wafer W. Effects of the inherent parameters of the camera 1 will be described later.
There is the possibility that the accuracy of defect inspection is deteriorated if a greatly distorted image is displayed on the output screen. Therefore, efforts are made to install the camera 1 in the inspection module such that the distortion of the image can be reduced to the least possible extent. A coordinate system shown in FIG. 17 has an origin o at the optical center o of the camera 1, a Zc-axis aligned with the optical axis of the camera 1, and an Xc-axis and a Yc-axis perpendicular to the Z-axis. In FIG. 17, α′, β′ and γ′ are angular displacements about the Xc-axis, Yc-axis and the Zc-axis, respectively. Correct positioning of the camera 1 so that the distortion of the image may be reduced to the least possible extent requires the adjustment of positions with respect to the Xc-axis, Yc-axis and the Zc-axis, and the angular displacements α′, β′ and γ′, which needs much time and labor.
Since many positioning parameters need to be adjusted, the positioning parameters representing the respective positions of different cameras adjusted by different operators are liable to be slightly different. Positioning parameters representing the optimum position and attitude of one of the cameras for forming an optimum image cannot be necessarily properly applied to determining the position and attitude of the other cameras for forming an optimum image if different cameras have different parameters, such as the distortion of the lens, respectively. Those problems increase time necessary for installing the camera 1 and can be causes of increase in the degree of distortion of the image and failure in achieving correct inspection.
Defect inspection can be achieved through the examination of the image displayed on the output screen by the operator. Generally, defect inspection is achieved through the comparison of image data on the image of the wafer W formed by the image forming device 12 with reference image data on a reference wafer W having an ideal morphology stored in the storage device of a computer. However, image data obtained by different cameras are different because different cameras have different positioning errors, respectively. Therefore, different substrate inspection systems need to store different reference image data, respectively. If reference image data prepared for a first substrate inspection system is used by a second substrate inspection system, there is the possibility that the computer of the second substrate inspection system mistakenly decide that a practically perfect part of a wafer W is defective. The preparation of different optimum reference image data for different substrate inspection systems requires much work.
In some cases, common reference image data is used by different substrate inspection systems. In such a case, detection sensitivity is lowered to avoid such an incorrect decision and the substrate inspection system tolerates measured image data greatly different from the reference image data and decides an image represented by the measured image data to be acceptable. The substrate inspection system that inspects wafers in such a mode cannot achieve accurate inspection.
Any means for solving those problems is not mentioned in JP-A 2007-240519. JP-A 2007-93330 proposes a technique for correcting the distortion of an image due to errors in the adjustment of the optical system of a substrate inspection system by processing a measured image for correction. However, any method of carrying out the correction is not mentioned in JP-A 2007-93330 and hence the technique cannot solve the foregoing problems.